This application claims the benefit of Korean Application No. P2000-17402 filed Apr. 3, 2000, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a low-resistance gate transistor and a method for fabricating the same, in which a metal sidewall is formed at sides of a gate poly-silicon layer to reduce a resistance and a height of a gate, thereby improving performances of a semiconductor device.
2. Background of the Related Art
With reference to the accompanying drawings, a related art semiconductor device will be described.
FIG. 1 is a section showing a related art transistor;
In a memory such as DRAM, and a logic device, a gate resistance causes reduction of a gate capacitance and RC delay of an input signal.
The gate resistance is inevitably caused by a thickness of a gate oxide film, but the solution to this problem is restricted.
Accordingly, in order to overcome the problem of RC delay of an input signal, methods in designing a semiconductor device are under study for reduction of the gate resistance, typically by forming a polycide layer, such as W, Ti, Co, on a gate poly-silicon layer, or depositing a metal, such as W, on the gate poly-silicon layer, to form a gate.
The related art transistor is provided with a semiconductor substrate 1; a gate oxide film 2 formed on the semiconductor substrate 1; a gate poly-silicon layer 3 and a metal layer 4 formed on the gate oxide film 2 in succession; LDD (Lightly Doped Drain) regions 7 formed in a surface of the semiconductor substrate 1 on both sides of a gate line of a stack of the gate poly-silicon layer 3 and the metal layer 4, and aligned with the gate line 1; gate sidewalls 5 formed at sides of the gate poly-silicon layer 3 and the metal layer 4 over the LDD regions; and deep source/drain regions 6 formed in the surface of the semiconductor substrate 1 on both sides of the gate line to be aligned with the gate sidewalls 5.
The foregoing related art transistor has a metal layer 4 formed on a gate poly-silicon layer 3 for reducing the gate resistance for solving the problem of RC delay of an input signal.
The deposition of a polycide layer and a metal layer for reducing the gate resistance results in a structure of gate polysilicon layer+gate polycide layer, or gate poly-silicon layer+metal layer+gate cap dielectric layer, with an increased stack height.
However, the related art transistor employed as a semiconductor memory device or a logic device has the following problems.
The deposition of a polycide layer and a metal layer for reducing the gate resistance increases a total height of the gate. This in turn reduces a fabrication allowance of a following process thus dropping fabrication efficiency.
Particularly, the fabrication efficiency drop in a case of tilted ion injection generally used for extending a halo ion injection region to an inside of a channel, deteriorates the reproducibility and performance of the device, and drops a device""s reliability.
Accordingly, an object of the present invention is to solve at least the problems and disadvantages of the related art.
Another object of the present invention is to provide a low-resistance gate transistor and a method for fabricating the same, in which a metal sidewall is formed at sides of a gate poly-silicon layer to reduce the resistance and the height of a gate, thereby improving performances of a semiconductor device.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims.
To achieve the objects and in accordance with the purposes of the invention, as embodied and broadly described herein, a low-resistance gate transistor includes a gate oxide film formed on a semiconductor substrate; a gate formed on the gate oxide film; a first gate sidewall having a vertical pattern in contact with a side of the gate at both sides of the gate and a horizontal pattern formed on the gate oxide film extended from the vertical pattern; second gate sidewalls formed of a material having resistivity lower than the gate, each having one side in contact with the vertical pattern of the first gate sidewall and a bottom in contact with the horizontal pattern of the first gate sidewall with a round surface; an insulating layer formed on an entire surface including the gate and the first and second gate sidewalls; and, source/drain regions formed in a surface of the semiconductor substrate on both sides of the gate.
A method for fabricating a low-resistance gate transistor according to the invention includes steps of: forming a gate oxide film on a semiconductor substrate, and forming a gate thereon; forming a lightly doped impurity region in the surface of the semiconductor substrate using the gate as a mask; forming a layer of a material the same as the gate on an entire surface including the gate to a fixed thickness; forming a layer of a material having resistivity lower than the gate on an entire surface, and patterning the layer of a material the same as the gate and the layer of a material having resistivity lower than the gate to form a first sidewall and a second sidewall; and forming a gate protection insulating layer on an entire surface, and injecting impurity ions heavily to form heavily doped impurity regions in the surface of the semiconductor substrate.